I would drop the trigger group, and check the interlock/butterfly screw. It could have backed out on you, since you say that this barrel/frame combo worked in the past. If that is the problem, a dab of Loctite (blue) is in order. While you have it apart, it would be a good time for a thorough cleaning, as well. You may have gotten a bit of debris where it shouldn't be. You can check engagement of the lugs at this time, too. Don't forget to clean the lugs & recesses on the barrel, too, since you state this problem follows the barrel, when switched to a different frame. It is likely that the lugs on your barrel were bordering on being too thick for the frame which worked previously. A light stoning may be in order. Hope this helps,,,,,,,,,,,,,,,,,,,,,,,,Bug.